Hair loss is of concern to a large number of men and women. In many individuals, hair loss (i.e., alopecia) causes embarrassment, and/or psychological problems such as depression. Although alopecia is more common in men (e.g., male pattern baldness or androgenic alopecia) than women (e.g., female pattern baldness), it is a significant concern to both men and women. Indeed, millions of dollars and countless hours of research have been dedicated to solving this problem.
The mature hair follicle is a complex mini-organ that has a tightly regulated growth cycle. During postnatal development, the follicle undergoes successive phases of active hair shaft production (anagen), apoptosis-driven regression (catagen), and a quiescent phase (telogen). Paus et al., “The biology of hair follicles,” NEJM 341:491-497 (1999). During the anagen phase, active hair growth involves cell proliferation in the proximal follicular epithelium, followed by invasion of the elongating follicle into the subcutaneous tissue, differentiation of the epithelium at the base of the follicle, and formation of hair matrix cells, which proliferate and generate a new hair shaft. When the proliferation capacity of the matrix cells is exhausted, a regression phase (catagen) of the hair growth cycle ensues, through which the lower part of the follicle undergoes programmed cell death and involution. Costsarelis et al., “The hair follicle: dying for attention,” Am. J. Pathol. 151:1505-1509 (1997). At this point, the follicle enters telogen, the resting period. The cycle is then repeated.
Scalp hair follicles cycle independently of each other. On average, of 100,000 scalp hairs, approximately 90% are in the anagenic (i.e., growth) phase, while the remaining 10% are in the telogenic (i.e., resting) phase, at any given point in time. Whiting, “Disorders of Hair,” in Dale and Federman (ed.), Scientific American Medicine (from Web MD Scientific American Medicine), New York (1999), pages 2:XIII:1-7. The anagen phase lasts an average of about three years, with a range of one to seven years, while the telogen phase lasts an average of about three months, after which the resting hairs are shed and new hairs grow in. The average rate of scalp hair growth is approximately 0.35 mm/day (i.e., approximately 1 inch every 2-3 months). In the anagenic phase, the cells surrounding the dermal papilla actively divide approximately every 12 hours, in order to produce cells which line up, grow longer, and begin to keratinize. During a transition stage (i.e., the catagenic or regression phase) that occurs between the anagen and telogen phases, mitosis no longer occurs and the bulb detaches itself from the papilla and rises towards the surface. In the telogenic phase, the hair is fully keratinized and is ready to be expelled. After three to four months, another mitotic cycle begins in the germination zone of the hair and another hair follicle is formed.
An average loss of 100 scalp hairs/day is considered to be normal, with a higher number being shed on days when the hair is washed. In diagnosing hair disorders, it is important to determine whether the shedding is abnormal and whether shed hairs break off or come out by the roots. Hair normally comes out by the roots. However, trauma or excessive fragility of the hair may cause it to break. In examination of patients, hair pull tests may indicate abnormal shedding. In this test, groups of 10-20 hairs are grasped between the index finger and thumb and pulled steadily. Extraction of more than 20% of the grasped hairs potentially indicates abnormal shedding, usually involving telogen hairs. Telogen hairs (“club hairs”) are easily recognized, due to their whitish club-shaped bulbs and lack of root sheaths. Normally, anagen hairs are difficult to detach and have blackish, indented roots with intact root sheaths (Whiting, Web MD Scientific American Medicine, pages 2:XIII:1-7 (1999)).
There are various forms of alopecia observed in humans. The most common is androgenetic alopecia, although diffuse alopecia, telogen effluvium, anagen effluvium (i.e., anagen arrest), alopecia areata, traumatic alopecia, trichotillomania, cicatricial alopecia, and other types of hair loss are also observed. In addition, hair loss associated with cancer treatment is quite common and of great concern to a large number of patients. Indeed, treatment with various drugs (e.g., alpha blockers, angiotensin converting enzyme inhibitors, anticoagulants, anticonvulsants, antithyroids, beta blockers, calcium channel blockers, cholesterol reducers, H2 receptor blockers, non-steroidal anti-inflammatories, retinoids, retinol, tricyclic antidepressants, etc.) can result in hair loss for a significant number of patients.
Depending upon the severity, treatment and management of alopecia ranges from continuing observation to medical and surgical treatment, to use of a hairpiece or wig. Topical 2% minoxidil has been approved by the U.S. Food and Drug Administration for use in both men and women. It produces visible hair growth in approximately ⅓ of male and female androgenetic patients, fine-hair growth in approximately ⅓ of patients, and no hair growth in approximately ⅓ of patients. However, it appears to be a relatively effective preventative treatment, as it retards hair loss in approximately 80% of patients. Whiting, Web MD Scientific American Medicine, pages 2:XIII: 1-7 (1999). Topical 5% minoxidil produces visible hair growth in 45% of male androgenetic alopecia patients in a shorter time than the 2% solution. Side effects of minoxidil administration include scalp irritation and increased facial hair. In addition, the drug should be used for at least one year to assess whether or not it is effective. If it is effective, use of the medication must be continued indefinitely.
Other compounds that have found use include orally administered finasteride (1 mg/day). At a dosage of 1 mg/day given for 2 years to male patients between 18 and 41 years of age, visible hair growth was observed in 66% of cases and further hair loss was prevented in 83%. Whiting, Web MD Scientific American Medicine, pages 2:XIII: 1-7 (1999). However, administration to post-menopausal women was found to be ineffective at a 1 mg/day dosage given over a 1 year period. Side effects of finasteride include lack of libido, lack of potency, and mild reduction in semen. Because of potential severe teratogenic problems for male fetuses, the drug is contraindicated for use by pre-menopausal women.
Additional drugs for treating androgenetic alopecia in women include oral contraceptives (e.g., ethinyl estradiol-ethynodiol diacetate, desogesterl-ethynyl estradiol, and ethinyl estradiol-norgesterimate), which can reduce hair loss and sometimes lead to slight hair growth. Whiting, Web MD Scientific American Medicine, pages 2:XIII: 1-7 (1999). Oral spironlactone and dexamethasone have also found use in treatment of female patients.
For other types of alopecia, various approaches include anthralin, psoralen and ultraviolet A, steroids, topical immunotherapy, immunosuppressives, long-term antimicrobial treatment, etc. However, some of these treatment regimes present risks and associated side effects, some of which may be severe.
In cases that do not respond to these compositions, hair transplantation with minigrafts or micrografts may be an option for patients with good reserves of hair on the back and sides of the scalp. In other cases, a hairpiece is the primary option. Indeed, despite the large commitment of resources in the quest for successful treatment and prevention of hair loss, all previously known treatments suffer from serious disadvantages. Thus, there remains a need for compositions and methods to promote hair growth.
The ability of hair follicles to constantly renew is ensured by the presence of multipotent stem cells which, upon division, generate two types of daughter cells. Some of the daughter cells retain the same multipotent phenotype, while others become rapidly-dividing transit-amplifying (TA) cells, which provide differentiated progeny for the regeneration of the lower follicle at the onset of each new cycle and formation of the hair shaft. Janes et al., “Epidermal stem cells,” J. Pathol. 197:479-494 (2002). Recently, the bulge region of the follicle, located close to the insertion of the arrector pili muscle, has been identified as a stem cells “niche.” See Lyle et al., “Human follicle bulge cells are biochemically distinct and possess an epithelial stem cell phenotype,” J. Invest. Dermatol Synip. Proc. 4:296-301 (1999); Taylor et al., “Involvement of follicular stem cells in forming not only the follicle but also the epidermis,” Cell 102:453-461 (2000); Oshima et al., “Morphogenesis and renewal of hair follicles from adult multipotent stem cells,” Cell 104:233-245 (2001). At the onset of anagen, bulge-localized, multipotent stem cells or their TA daughter cells migrate to the base of the follicle to become matrix cells and to produce a new hair shaft. Interestingly, cells emanating from the bulge region migrate downward to repopulate the hair matrix and also migrate upwards to replenish the skin epithelium, and may therefore contribute to wound healing processes.
Thymosin β4, an ubiquitous 4.9 kDa polypeptide originally isolated from bovine thymus, is a potent mediator of some types of cell migration and differentiation. See Low et al, “Complete amino acid sequence of bovine thymosin: a thymic hormone that induces terminal deoxynucleotidyl transferase activity in thymocyte populations,” Proc. Natl. Acad. Sci. 78:1162-1166 (1981); Grant et al., “A novel role for thymosin beta4: a Matrigel-induced gene involved in endothelial cell differentiation and angiogenesis,” J. Cell Science 108:3685-3694 (1995); Malinda et al., “Thymosin β4 stimulates directional migration of human umbilical vein endothelial cells,” FASEB J. 11:474-481 (1997); Malinda et al., “Thymosin β4 accelerates wound healing,” J. Invest. Dermatol. 113:364-368 (1999); Sosne et al., “Thymosin beta 4 promotes corneal wound healing and decreases inflammation in vivo following alkali injury,” Ex. Eye Res. 74:293-299 (2002). Thymosin β4 was identified with a gene that is upregulated four- to six-fold during early endothelial cell tube formation and was later shown to promote angiogenesis. It is present in wound fluid, and when added topically or given systemically it promotes angiogenesis and wound healing. See Frohm et al., “Biochemical and antibacterial analysis of human wound and blister fluid,” Eur. J. Biochem. 237:86-92 (1996); Malinda et al., J. Invest. Dermatol. 113:364-368 (1999). It is also a potent anti-inflammatory. Sosne et al., Ex. Eye Res. 74:293-299 (2002); Frohm et al., Eur. J. Biochem. 237:86-92 (1996); Young et al., “Thymosin beta 4 sulfoxide is an anti-inflammatory agent generated by monocytes in the presence of glucocoticoids,” Nat. Med. 5:1424-1427 (1999). Moreover, thymosin β4 is present at increased levels in metastatic tumors and when transfected into low metastatic cells, it increases malignancy. Clark et al., “Genomic analysis of metastasis reveals an essential role for RhoC,” Nature 406:532-535 (2000); Kobayashi et al., “Thymosin-beta4 regulates motility and metastasis of malignant mouse fibrosarcoma cells,” Am J. Pathol. 160:869-882 (2002). A related family member, thymosin β15, is also important in metastasis of certain tumor types. Bao et al., “Thymosin beta 15: a novel regulator of tumor cell motility upregulated in metastatic prostate cancer,” Nat. Med. 2:1322-1328 (1996); Bao et al., “Thymosin beta 15 expression in tumor cell lines with varying metastatic potential,” Clin. Exp. Metastasis 16:227-233 (1998). The metastatic activity of thymosin β4 may be related to its angiogneic and migration-promoting activities as well as to its potential to inhibit immune surveillance. Recently, thymosin β4 was found to be a potent antimicrobial. Tung et al., “Antimicrobial peptides from human platelets,” Infect. Immnwz. 70:6524-6533 (2002).
Thymosin β4 typically acts by accelerating the migration of endothelial cells and keratinocytes, and increasing the production of extracellular matrix-degrading enzymes.